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Stoichiometry
The Balanced Chemical Reaction
A balanced chemical reaction can be
interpreted in two ways. First, it can be
thought of as describing how many
molecules (or atoms or formula units) of
reactants are consumed in order to produce
a certain number of molecules of products.
Analogously, it can be thought of as
describing how many moles of reactants are
consumed in order to produce the indicated
number of moles of products.
CuO(s) + H2(g) → Cu(s) + H2O(g)
How many H2O molecules are
produced for every H2 molecule that
is consumed in this reaction?
CuO(s) + H2(g) → Cu(s) + H2O(g)
How many H2O molecules are
produced for every H2 molecule that
is consumed in this reaction?
1
2CO(g) + O2(g) → 2CO2(g)
How many CO2 molecules are
produced for every O2 molecule
consumed?
2CO(g) + O2(g) → 2CO2(g)
How many CO2 molecules are
produced for every O2 molecule
consumed?
2
2CO(g) + O2(g) → 2CO2(g)
How many CO2 molecules are
produced for every CO molecule
consumed?
2CO(g) + O2(g) → 2CO2(g)
How many CO2 molecules are
produced for every CO molecule
consumed?
1
2CO(g) + O2(g) → 2CO2(g)
How many molecules of CO2 are
produced when 2 molecules of O2
are consumed?
2CO(g) + O2(g) → 2CO2(g)
How many molecules of CO2 are
produced when 2 molecules of O2
are consumed?
4
2CO(g) + O2(g) → 2CO2(g)
How many moles of CO2 are
produced when 5 moles of O2 are
consumed?
2CO(g) + O2(g) → 2CO2(g)
How many moles of CO2 are
produced when 5 moles of O2 are
consumed?
10
CuO(s) + H2(g) → Cu(s) + H2O(g)
How many moles of CuO react in
order to produce 12 moles of Cu?
CuO(s) + H2(g) → Cu(s) + H2O(g)
How many moles of CuO react in
order to produce 12 moles of Cu?
12
Determine the number of reactant
molecules and the number of product
molecules for each reaction:
CuO(s) + H2(g) → Cu(s) + H2O(g)
2CO(g) + O2(g) → 2CO2(g)
Determine the number of reactant
molecules and the number of product
molecules for each reaction:
CuO(s) + H2(g) → Cu(s) + H2O(g)
2 reactant and 2 product
2CO(g) + O2(g) → 2CO2(g)
3 reactant and 2 product
Is the number of molecules identical
on the reactant and product sides of
these balanced reactions?
CuO(s) + H2(g) → Cu(s) + H2O(g)
2CO(g) + O2(g) → 2CO2(g)
Is the number of molecules identical
on the reactant and product sides of
these balanced reactions?
CuO(s) + H2(g) → Cu(s) + H2O(g)
2CO(g) + O2(g) → 2CO2(g)
No
Does the total number of moles of
gas increase, decrease, or remain
constant for this reaction?
2CO(g) + O2(g) → 2CO2(g)
Does the total number of moles of
gas increase, decrease, or remain
constant for this reaction?
2CO(g) + O2(g) → 2CO2(g)
Moles decrease.
(Moles are not conserved.)
No Whiteboard
How is this consistent with the idea
that atoms are neither created nor
destroyed when a chemical reaction
takes place?
CuO(s) + H2(g) → Cu(s) + H2O(g)
Is it correct to state that if 100 grams
of CuO are consumed when the
reaction occurs, then 100g of Cu are
formed in the process? Why or why
not?
No Whiteboard
2CO(g) + O2(g) → 2CO2(g)
Describe in complete sentences the
steps taken to calculate the number
of grams of CO2 produced in this
reaction given that X grams of O2 are
consumed.
Stoichiometry
• Stoichiometry is a quantitative description
of a chemical reaction. It involves
determining the amounts of reactants and
products in a chemical reaction. It is based
on the balanced chemical equation.
• Stoichiometry answers “How much?”
Mole Ratio
• A mole ratio is a conversion factor used in
stoichiometry. It is the ratio of moles of one
reactant or product to another reactant or
product based on the coefficients of a
balanced chemical equation. It allows you
to convert moles of one substance to
moles of another substance in a chemical
reaction.
2CO(g) + O2(g) → 2CO2(g)
4 moles of O2 will react to form how many moles
of CO2 according to the above chemical
equation?
4 mol O2 x 2 mol CO2 = 8 mol CO2
1 mol O2
Mole Ratio!
Practice
Al + CuSO4 → Al2(SO4)3 + Cu
Practice
2Al + 3CuSO4 → Al2(SO4)3 + 3Cu
Remember! You must always use a
balanced chemical equation for all
stoichiometry problems.
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